Device for varying the tension of the bottom thread on the bobbin housing of a sewing machine



1959 E. SCHENKENGEL DEVICE FOR VARYING THE TENSION OF THE BOTTOM THREAD ON THE BOBBIN HOUSING OF A SEWING MACHINE Filed NOV. 21, 1957 IN VENTO I? Emerich SCHENKENGEL A'gavr United States Patent O i DEVICE FOR VARYING THE TENSION OF THE BOTTOM THREAD ON THE BOBBIN HOUSING OF A SEWING MACHINE Emerich Schenkengel, Kaiserslautern, Pfalz, Germany, .assignor to G. M. Pfalf AG, Kaiserslautern, Pfalz, Germany Application November 21, 1957, Serial No. 697,879 '1 Claim. (Cl. 112-233) The invention relates to sewing machines and is particularly concerned with means for controlling the tension of the bottom thread.

It is known for controlling the passage of the bottom thread to employ a spring provided on the bobbin housing of the sewing machine the tension of which can be changed by means of an adjusting screw. Heretofore a simple slotted screw was used in most instances which requires a screw driver for tightening or loosening.

A screw driver is not always available in a household and, moreover, many women do not like to manipulate tools. For that reason, the heads of the screws regulating the passage of the thread have already been provided with knurled edges around their circumference to permit seizing them more conveniently with the fingers to make adjustments without the use of a tool.

In known designs of this type the screw heads were enlarged considerably. However the enlargement of the head of the adjusting screws is confined to close limits because the space between the housing of the bobbin and of the looper moving about it is extremely limited and because, moreover, there is the danger of collision between the upper thread guided by means of the looper around the bobbin housing and the enlarged head of the adjusting screw provided with an edging.

It is an object of the invention to form the means which make it possible to change the tension of the lower thread in a manner that the tension of the lower thread can likewise be changed without tools but more finely and reliably while at the same time making it unnecessary to change the dimensions of the bobbin housing and of the looper which have proven so satisfactory for many years.

In accordance with the invention the head of the adjusting screw which acts on the spring which controls the passage of the lower thread is provided with an edging of a special type, a so-called crown knurled edge and at the same time the head proper is formed in such a manner that it is disposed in the space around which the loop of the upper thread moves while avoiding any contact therewith.

In accordance with the invention the shaping of the head of the set screw makes it possible to pick up the bobbin housing in one hand and by simple turning of one finger of the other hand, for example the index finger, about its longitudinal axis to control the tension of the bottom thread in simplest fashion and yet with the most delicate feeling. That is a most significant advantage which becomes still more apparent if, as proposed in accordance with the invention, an indentation is provided on the front end of the head of said setting or adjusting screw the deepest place of which is in the center of the front end and which flattens out toward the edge. The finger tip then encounters an especially good engagement surface for turning the adjusting screw.

Since it may happen that the adjusting screw turns with relative difficulty it may be desirable to provide a possibility to assist occasionally with a tool. It is, therefore, a further object of the invention to provide a slot Ice 2,901,292

Patented Oct. 6, 1959 2 in the head of the adjusting screw the base of which is provided with an arcuation having a radius corresponding to that of the outer periphery of the'flange of the bobbin. Thus, if the adjusting screw could not be turned with the finger for one reason or another it is possible in such an emergencyto use the bobbin asan immediately and readily available screw driver.

Other objects of the invention and details regarding the advantages obtained thereby .will become apparent from the following description'of the embodiment of an arrangement for varying the tension of thebottom thread illustrated in the drawings in which Fig. l is a perspective view of the complete device,

Fig. 2 shows the adjusting screw separately drawnto, a larger scale and partly in cross-section.

Fig. 3 is a detail of the adjusting screw with a portion of the spring which controls the passage of the thread, and

Fig. 4 is a perspective view of the entire bobbin housing disposed in a looper.

The housing 1 receives the bobbin 5 in which the bottom thread is wound. A leaf spring 3 is secured on the outside of this housing by means of a screw 2 having its head sunk into the housing. The other end of the spring 3 which is elastic, due to the one sided mounting is located above a slot 4 which is provided in the housing and permits the bottom thread 6 drawn from the bobbin to pass through. The thread is passed below the spring 3 and in this connection the force required to draw the bottom thread 6 out depends on the pressure applied by spring 3 upon the thread. This pressure, in turn, is adjustable by means of an adjusting screw 7 (Figs. 2 and 3) which is threadedly mounted in the wall of the bobbin housing 1.

The head 8 of the adjusting screw 7 is provided with a special edging 10 as indicated in Figs. 2 and 3, which is known in the art as crown edging. The head 8 is furthermore formed in such a manner that it is disposable in the area swept by the loop 13 of'the upper thread while avoiding any contact therewith.

The front end of the head 8 of adjusting screw 7 is provided with an indentation 11 the nadir of which is in the center of the head 8. As shown in Fig. 2, the indentation flattens out towards the border.

The upper thread 13 drawn by the looper 12 can unimpededly pass the head 8 of the adjusting screw 7 without touching the same.

It may be desirable to provide an inclined border 14 which may extend parallel to the passing upper thread 13. This provides additional assurance for the free course of the upper thread 13. The said inclined border edging 14 is of particular advantage if it is combined with a recess in the thread passage controlling spring 13 as reflected by the illustration in Fig. 3 which is drawn to an enlarged scale. The spring 3 has an aperture here the border of which is beaded in such a manner that the head 8 of the screw 7 is embedded in the bead so that the head 8 of screw 7 does not project at all above the outline of the aperture or only to a minimum extent.

The head 8 of adjusting screw 7 is provided with a slot 15 (Figs. 2 and 3) the base of which has an arenation which corresponds to the outer periphery of the flange of the bobbin 5. The flange of the bobbin can be inserted in this slot if it should be desirable or necessary in an exceptional case to use a tool for turning screw 7. In that event the bobbin 5 constitutes a tool which is ready at hand.

Having now described the invention with reference to the embodiment illustrated in the drawing I claim:

Means for varying the tension of the bottom thread in a sewing machine of the type having a looper and a bobbin housing received in the looper, said means being a 3 adapted to avoid contact with the upper looper thread and comprising, in combination, the bobbin housing, a leaf spring mounted externally of the bobbin housing and haying a raised outwardly curved portion, a threaded aperture in said housing, a tensioningscrew aperture in said raised curved portion of said leaf spring in registering reiation to said threaded aperture, a circular beaded portion extending around said tensioning screw aperture having an inwardly and downwardly extending portion defining a seat for a screw head and an adjusting screw having a threaded portion extending through said tensioning screw aperture and into said threaded aperture for appiying variable pressure to said spring and thereby to the bottom thread, said screw having a head disposed on said-seatwithin the looper for movement in the area of looper thread movement, said head having an upper outer annular portion tapering outwardly and downwardly and having radially extending grooves formed therein,

and having an indented central portion, said annular portion and said central portion intersecting to form a circular crest at a height substantially the same as that of the crest of said head defined by teeth intermediate said grooves presenting a frictional engagement are for digital actuation, and a slot defined transversely of the head of said screw having an arcuation based on a radius corresponding to that of the outer periphery of the flange of said bobbin.

References-Cited in the fileof this patent UNITED STATES PATENTS 1,120,403 OLeary Dec. 8, 1914 1,879,023 Barron Sept. 27, 1932 1,898,202 Murray -2 Feb. 21, 1933 2,110,947 Bartels Mar. 15, 1938 2,760,400 Mills et a1. r t Aug 28, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,907,292 October 6, 1959 Emerich Schenkengel It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters .Patent should read as corrected below.

Column 4, line 5, for "are for" read area for ------a Signed and sealed this 17th day of May 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

